There is no substitute for persistence. You must get all the training you need, and you must do well at it... that's a given. But in order to succeed in this business, the most important thing is to not let setbacks stop you.
Get both MER rovers to Mars, operate them successfully, and then get a lot of rest!
Sending humans to Mars, the sooner the better.
I realized that this was what I wanted to do as an undergraduate in college, when I took a course on the results of the Viking mission to Mars. At that point I changed my main subject of study from geology to space science, and I have done nothing else ever since.